High frequency electron discharge devices of the klystron type incorporating below cut-off waveguide leaky wall h-field tuners



June 25. 1968 D. MACK 3,390,300

SCHARGE DEVICES OF THE TIN HIGH FREQUENCY EL RON DI ELOW -OFF KLY ON TYPE INCORPORA EGUIDE LEAKY WALL 8- LD TU S 2 Sheets-Sheet 1 Filed Oct. 22, 1965 FIG.5

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INVENTOR x CHARLES D. MACK f BY - W 28l6 41 ORNEY June 25. 1968 c. D. MACK 3,390,300

HIGH FREQUENCY ELECTRON DISCHARGE DEVICES OF THE KLYSTRON TYPE INCORPORATING EELow CUT-OFF WAVEGUIDE LEAKY WALL H-FIELD TUNERS Filed Oct. 22, 1965 2 Sheets-Sheet 2 g 40 E INVENTOR. 3 CHARLES D. MACK FREQUENCY (G C) United States Patent 3,390,300 HIGH FREQUENCY ELECTRON DISCHARGE DE- VICES OF THE KLYSTRON TYPE INCORPORAT- ING BELOW CUT-OFF WAVEGUIDE LEAKY WALL H-FIELD TUNERS Charles D. Mack, San Jose, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Oct. 22, 1965, Ser. No. 500,970 14 Claims. (Cl. 3155.21)

This invention relates to high frequency electron discharge devices and more particularly, to high frequency electron discharge devices of the klystron type having improved tuner mechanisms.

The prior art is replete with methods of mechanically tuning high frequency electron discharge devices of the klystron type such as for example by means of tunable external cavities coupled to a klystron cavity to form an internal-external cavity resonator and by means of locating various tuning screws, probes and plungers in waveguides coupled to the klystron cavity of interest, movable diaphragms, walls etc. As the operating frequency of klystrons such as for example a reflex klystron approach higher and higher frequencies, eg the upper kilomegacycle ranges such as for example 1 to 100 gigacycles, the problem of dimensional parameters becomes acute. By that we mean the cavity dimensions become minutely small and it becomes extremely diflicult, for example, to utilize external cavity or conventional waveguide tuning mechanisms without greatly increasing the cost of the klystron.

The present invention provides an improved tuning mechanism for klystrons such as the reflux klystron, the coupled cavity klystron oscillator and tunable multicavity klystron amplifiers which incorporate a leaky wall waveguide H-field perturbing tuner concept wherein a simple waveguide which is cut off at the operating mode (fundamental mode) resonant frequency of the klystron cavity to be tuned is coupled through an aperture in the cavity Wall via an electromagnetic wave permeable dielectric window vacuum sealed across the aperture. The presence of the dielectric window increases the available electromagnetic H-field strength within the cut-off waveguide tuning section thereby increasing the tuning range for the tuner under consideration.

The particular advantages to be derived from the teachings of the present invention are: facilitation of klystron construction especially at the upper frequency ranges; the ability to construct entire families of a given tube to cover a broad frequency spectrum without redesigning the cavity dimensions; simplified fabrication and simplified parts utilized for the tuner mechanism; the elimination of bellows, diaphragms, etc. which heretofore limited tuner life; elimination of vacuum leakage through diaphragm to cavity joints etc.; elimination of frequency jumping between plural modes such as are found in internal-external cavities and in propagating waveguides under certain conditions where the resonant frequency of a higher order mode is moved down by tuning to the low end of the band; and resultant elimination of mechanisms which are conventionally used for suppressing such modes other than the operating mode.

A typical example of a prior art external cavity tunable klystron which requires mode suppression means to prevent frequency jumping is US. Patent No. 2,880,357 by D. L. Snow et al. A typical example of a klystron incorporating a propagating waveguide for tuning purposes is US. Patent No. 2,829,352 by S. R. Hennies et al. The present invention obviates the aforementioned problems by utilizing what may be termed a simple leaky wall inductive tuner scheme wherein a wave- 3,390,300 Patented June 25, 1968 guide having either a dielectric or metallic movable tuning member is coupled through an aperture in the high current (high H-field portion of the klystron cavity side wall) via a dielectric wave permeable window member with the waveguide having a cut-off frequency for any modes capable of being coupled thereto which is below the tunable frequency band of the fundamental mode of operation. By making the waveguide cross-sectional dimensions to have a dominant mode cut-off frequency which is above the highest operating frequency over the tunable band of the fundamental operating mode R.F. leakage problems are reduced, and coupled cavity mode jumping problems between A2 and 3M2 modes are obviated.

It is therefore an object of the present invention to provide an improved tunable klystron electron discharge device.

A feature of the present invention is the provision of a high frequency electron discharge device of the klystron type incorporating a leaky wall I-I-field perturbing tuning means.

Another feature of the present invention is the provision of a high frequency electron discharge device of the klystron type incorporating a tuning means including a leaky wall H-field perturbing cut-off waveguide coupled through an electromagnetic wave permeable dielectric window disposed across an aperture in a resonant cavity of said klystron said cut-off waveguide being provided with a movable tuning element.

Another feature of the present invention is the provision of a klystron electron discharge device having at least one resonant cavity of the re-entrant type operable in the fundamental mode and having an aperture in the side wall thereof which aperture is surounded by a circular waveguide which has a cut-off frequency for the TE mode which is above the highest operating frequency of the tunable bandwidth of the fundamental operating mode of the re-entrant type resonant cavity, said waveguide being provided with a movable tuner member which functions to vary the amount of H-field penetration into the circular waveguide.

Other objects and advantages of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary cross-sectional view of an illustrative reflux klystron incorporating the novel tuning mechanism of the present invention.

FIG, 4 is an alternative embodiment of the reflex klystron depicted in FIG. 1 wherein the dielectric window is disposed flush with the klystron tube main body wall.

FIG. 5 is an illustrative graphical portray-a1 depicting tuning range versus dielectric window thickness for a leaky wall H-field cutoff waveguide tuner mechanism of the klystron depicted in FIG. 1.

FIG. 2 is a fragmentary sectional view partly in elevation taken along the lines 22 of FIG. 1 in the direction of the arrows.

FIG. 3 is an alternative embodiment of the leaky wall H-field tuner mechanism employing a dielectric tuner screw member.

FIG. 6 is a graphical portrayal of Power out vs. tunable bandwidth for reflex klystrons embodying the tuning schemes depicted in FIGS. 7-9.

FIGS. 7-12 are alternative embodiments of the leaky wall H-field tuner mechanisms of the present invention.

FIG. 13 is a graphical portrayal of Power out vs. tunable bandwidth for reflex klystrons embodying the tuning schemes depicted in FIGS. 4 and l012.

FIGS. 14 and 15 depict a variation in the iris-window combinations depicted in FIG. 1.

Referring now to FIG. 1 there is depicted a fragmentary view in cross-section of a reflex klystron utilized as a representative example of high frequency electron discharge devices of the klystron type which incorporates at least one reentrant resonant cavity 16 which provides a beam-field inter-action vehicle between the electromagnetic fields of the fundamental mode of the cavity and an electron beam denoted by dashed lines traversing therethrough. Since the literature is replete on the operating mechanisms and design characteristics of klystrons such as the reflex klystron illustrated in FIG. 1, or coupled cavity oscillators and plural cavity amplifiers a thorough discussion of their operative nature will not :be set forth herein. See for example, Klystrons and Microwave Triodes, by Arnold R. Hamilton et al. Radiation Laboratories Series, Vol. 7, New York, McGraw-Hill Book Company, Inc., 1948.

In brief, the reflex klystron 15 includes an electron gun 18 of any conventional type such as a Pierce gun with focusing electrode 20 and cathode assembly 18' disposed at the downstream end portion thereof for producing and directing an electron beam through the re-entrant circularly symmetric resonant cavity 16 and into the reflector region 17 whence a suitable negative voltage on the reflector electrode 19 repels the bunched electrons in a conventional manner back through interaction gap g to gen erate a microwave signal. The reflector electrode 19 is supported by any suitable conductive rod member 21 disposed along the beam axis 22 and supported by means of any suitable dielectric disc 23 vacuum sealed across the tube main body 24 at the downstream end portion thereof. Similarly, the gun 18 utilized to generate the electron beam is supported by means of a dielectric disc 25 vacuum sealed across a copper or the like tube main body 24 at the upstream end portion thereof. The cathode 18' portion of gun 18 can be any known type such as for example an oxide coated button emitter type. The main body 24 is block shaped but can have any external shapes like a square, circle, rectangle etc. The side wall 26 of the cavity is shown as being generally circular to form a reentrant short gap circularly symmetric resonant cavity wherein the fundamental mode has maximum E-fields at the gap and minimum E-fields at the side walls, the H- fields being maximum at the sides and minimum at the gap. For optimum operation, klystrons are preferably operated at vacuum-s of 10- torr and lower. The cavity resonator 16 is of the re-entrant type as stated above and is defined at the ends thereof by a pair of axially spaced header members 27, 28, which form the cavity end walls which have axially aligned apertures 29, 30, therein and preferably provided with suitable grids 31, 32 for enhancing beam-wave coupling interaction. Several complex tuning schemes are depicted in the aforementioned Radiation Laboratories Volume beginning at page 508 and reference thereto is made to show the nature of and complexity of typical prior .art tuning schemes in addition to those set forth in the aforementioned US. patents.

The tuner mechanism 33 of the present invention includes a hollow circular waveguide 34 as of copper or the like vacuum :brazed in a conventional manner around a coupling aperture 35 in the side wall of the resonant cavity 16. The tuner mechanism 33 in the embodiment of FIG. 1 incorporates a metallic tuning screw 36 having external threads engaging the internal threads of the circular waveguide 34 as shown in FIG. 1. In order to enhance electromagnetic H-field penetration within the waveguide tuning section andto provide elimination of vacuum leakage problems a disc shaped dielectric window 37 as of alumina or the like having a thickness t is vacuum sealed across the oblong coupling aperture 35 and supported by means of a suitable cup shaped metallic support member 38 to complete the vacuum integrity for the klystron main body 24 as best seen in FIGS. 1 and 2. In operation, electromagnetic energy generated by the reflev klystron 15 is extracted via 'an output waveguide 40 having a suitable mounting flange member 41 for coupling to a load. A dielectric wave permeable alumina or the like window 42 preferably diametrically opposed to window 37 forms a vacuum seal for cavity 16 and is supported by means of a cup shaped support member 43 disposed about the coupling iris aperture 44 in a manner well known in the art.

In FIG. 4 an alternative window-coupling mechanism is depicted wherein the vacuum window 45 is disposed flush on the tube main body block 24 about the oblong iris 35 as shown. In other words, the dielectric window of the embodiment of FIG. 4 is disposed on top of the block body 24 :itself, and is brazed to a copper keeper washer 47 which in turn is brazed to the body and the bottom edge of circular waveguide 54. Reflex klystrons incorporating the tuner mechanism depicted in FIGS. 1 and 4 were built and tested and the following electrical characteristics resulted:

For a tube such as depicted in FIG. 1 using a circular dielectric window 37 having a diameter of .3 inch and a t dimension of .03 inch supported on a cup shaped support member such as 38 to vacuum seal an iris 35 having a major axis of .3 inch and a minor axis of .080 inch, a tuning range of from 13.120 gigacycles to 13.175 gigacycles or some 55 megacycles was achieved with a beam current of 30 milliampers and a resonator voltage of 300 volts operating on a peak power reflector mode with the reflector voltage varied to maintain operation at the center of the mode. A reflex klystron such as depicted in FIG. 1 incorporating a tuner mechanism such as depicted in FIG. 4 with the same dielectric window disposed directly on the body block within a .030 inch thick washer 47 disposed about the same iris was built and tested with a beam voltage of 300 volts, a beam current of 41 milliamps and a peak power reflector mode voltage variation between to 158 volts to operate at the center of the mode resulted in a mechanical tuning range of 235 megacycles (mc.) for P out (optimized) with mechanical tun-er position variations ranging from screw removed to screw against window.

The aforementioned tuning ranges were achieved with a waveguide internal ID. of .385 inch which was designed such that the operating frequency across the tunable bandwidth of the fundamental mode of cavity 16 was below the calculated cut-off frequency for the TE mode of propagation for circular guide. This of course precludes mode jumping problem-s of prior art couple-cavity internal-external tuned klystrons and also overcomes power loss problems and mode jumping which may occur in wide range propagating waveguide tuners. For example, klystrons operated at 60 milliwatts power output incorporating the below cut-off leaky wall H-field tuner concepts of the present invention were tested with the tuner screw such as 36 completely removed and radiated power out at the top end of the wave guide was only a .1 of a milliwatt with a inch L dimension. A tunable propagating waveguide may tune down sufliciently to lower the resonant frequency of a higher order mode sufficiently that mode jumping occurs. Furthermore the attenuation is purely reactive in the tunable guide of the present invention as opposed to the resistive attenuation of prior art propagating guide tuners.

Other advantages to be derived from utilizing a dielectric window in conjunction with a coupling iris and below cut-01f waveguide such as taught in each of the embodiments of the present invention are depicted in FIG. 5 wherein an illustrative graphical portrayal of tuning range represented by AP versus dielectric window thickness t for a representative dielectric window material such as alumina ceramic is depicted. An examination of the characteristic of FIG. 5 shows that indeed a minimal AF or relative tuning range is achieved for the case Where no window is present where-as a maximum AF is achieved for the case where a specific window dimension t such as denoted at the point of the curve marked X is present. Point X can be equated to a maximum H-field coupling-maximum tuning condition via the iris-window between the resonant cavity 16 and the circular waveguide 34. Thus it is self-evident upon examination of the AF versus 1 characteristic depicted in FIG. 3 that enchanced tuning range benefits are to be derived from the utilization of an electromagnetic wave permeable dielectric ceramic window in conjunction with a below cut-off leaky wall H-field waveguide tuning mechanism such as depicted herein. Furthermore, utilization of a dielectric vacuum window provides the additional advantage of maintaining vacuum integrity in a non-stressed portion of the tuning mechanism which obviously eliminates any leakage problems which are inherent in mov-able diaphragms, etc., which are conventionally utilized to maintain vacuum integrity. See for example, U.S. Patent No. 3,058,026 issued Oct. 9, 1962 by I. K. Mann et al. for a typical example of a tuning scheme employing a flexible diaphragm of limited life.

The portion of the curve of FIG. 5 marked X denotes the portion of maximum coupling-maximum tuning between the resonant cavity 16 and the cut-off waveguide 34. Point X can be characterized as a condition of resonance for the coupling iris-window combination between below cut-off waveguide 34 and resonant cavity 16 which is equivalent to saying a point of maximal tuning range AF is achieved for a given metal slug or screwtuner and window thickness t. The particular Window thickness t for maximum AF will vary with the window design and the precise thickness t to produce maximum AF can be determined on an empirical or experimental basis using known techniques for optimizing results.

In FIG. 3 another alternative tuner embodiment is depicted wherein a dielectric material such as Kel-F No. 300 fluorocarbon manufactured by the Minnesota Mining and Manufacturing Company is used to make the variable tuner screw member 50 in conjunction with a circular waveguide 34 having an internal diameter I.D. dimensioned such that the operating resonant frequency across the tunable bandwidth of the fundamental mode of cavity 16 is below the cut-of frequency for the TE mode of propagation for circular guide. The utilization of a dielectric tuner element or screw member 50 results in an inverted tuner motion vs. frequency characteristic in comparison to a metal tuner element or screw such as 36 tuner motion vs. frequency characteristic. In other words, the upper end-of the tunable band for a dielectric tuner exists when the tuner element or screw is completely retracted or removed from the waveguide 34 while the lower end of the tunable band for a dielectric tuner exists when the tuner element or screw is completely inserted within the waveguide 34.

In FIG. 6 curve B exemplifies the mechanical tuning range on a Power out vs. frequency characteristic (with the reflector voltage adjusted to operate at the center of the peak power reflector mode at each frequency) and with the arrow head indicating tuner direction into Waveguide for the dielectric tuner of the type depicted in FIG. 8. Of interest is the fact that maximum Power is achieved with the dielectric tuner screw removed and minimum Power is achieved with the tuner screw completely inserted into the waveguide. Also of interest is the fact that the high end of the mechanical tuning bandwidth occurs with the dielectric tuner screw completely retracted or removed from the waveguide. A tuning curve for the dielectric screw of the embodiment of FIG. 3 would have similar Power vs. frequency and tuner motion directional characteristics as curve B although obviously the range and slope would vary.

Turning now to FIGS. 7-9 there are depicted three alternative tuner embodiments utilized in conjunction with a circular leaky wall H-field waveguide coupled to a klystron such as depicted in FIG. 1. Similar reference numerals are used to indicate similar parts to avoid repetition. The circular waveguide denoted 54 is, practically speaking, identical to waveguide 34 of FIG. 1. with the exception of the copper washer 47 which is brazed to the body block 24 as previously described in connection with the embodiment depicted in FIG. 4 and with the addition of a reduced diameter internally threaded support flange portion 55 and the elimination of the internal threads along the guide length. The movable tuner screw 56 has a reduced diameter copper coated end tip 57 which provides the tuning characteristics depicted in FIG. 6 curve A wherein a better than 650 megacycle tuning range is achieved with an inverted Power vs. frequency tuning curve. In other words, the variation in Power and frequency with tuner motion is directionally similar to the dielectric embodiments with a. greatly extended tuning range. The aforementioned characteristics have been achieved with tip 0D. to waveguide I.D. ratios of approximately /3. As the ratio approaches unity the tuning characteristic slope approaches zero and then inverts. A zero tuning point with no tuning occurs at a critical point where the CD. of the tip approaches the CD. of the screw 56 which can be arrived at experimentally. The tuning characteristic A was obtained with a 300 volt beam voltage; 30 milliamp beam current over a center frequency of approximately 12.75 gc.; with L=.75 inches; CD. of tip=.125 inch; ID. of guide=.385 inch; the CD. of screw 56:.250 inch and the tip length L'=.325 inch; and the reflector voltage adjusted between -283 to 247 volts over the tunable band to obtain peak Power out by operating at the center of the peak power reflector mode for each frequency in the band.

In FIG. 8 another alternative embodiment dimensionally identical to FIG. 7 is depicted. The variation being the substitution of a dielectric tip 60 for the reduced copper plated tip 57 of the embodiment of FIG. 7. In FIG. 6 curve B represents the resultant tuning characteristic. The tuning range is considerably reduced while the slope or directionality characteristic remains the same for the /3 ratio and would probably show no change regardless of tip O.D. variation. Again the reflector voltage is adjusted to operate at the center of the peak power reflector mode over the tunable band.

In FIG. 9 another alternative tuner embodiment utilized in conjunction with at below cut-off waveguide is depicted. A M4 choke 61 is disposed on a reduced height end tip 62 mounted on screw 63 with determined at center frequency f0 of the tunable bandwidth. This particular tuner embodiment with a 13.25 f0; L=.75 inch; screw 63 CD. of .250 inch; guide ID. of .385 inch; beam voltage of 300,volts; 30 milliamps beam current and a reflector voltage variation from 230 to 305 volts over the tunable band to operate at peak power (the center of the peak power reflector mode) over the tunable band resulted in a flat Power out vs. frequency characteristic. In each embodiment incorporating a choke X is preferably determined at fo (the center frequency).

In FIG. 10 another alternative embodiment of a tuner utilized in conjunction with the cut-off guide 70 is shown. This tuner utilized a A/ 4 choke 71 in conjunction with a reduced diameter coupler rod 72 having a \/4 length between the bottom end of screw 73 and the top end of the choke 61. Again a copper washer 47 is brazed between the circular guide 70 and the main body block 24 with a circular window 45 brazed to the body 24 and the washer 74 to complete the vacuum seal for the klystron. With L=% in.; support rod O.D.=.175 inch; guide I.D.=.385 inch; beam voltage=300 volts; with a 41 milliamp beam current; and the reflector voltage varied between 153 to 168 volts to operate at the center of the peak power reflector mode over the tunable band the curve labeled D in the Power out vs. frequency characteristic resulted which has a 445 rnc. tunable band.

In FIG. 11 the reduced diameter support rod was reduced in length such that the electrical length between the top of the choke 61 and the bottom of tuner screw 81 was much less than US at the center of the operating band while L and the LB. and support rod O.D. remained fixed as discussed in connection with the embodiment of FIG. 10. With a beam voltage set at 300 v. and a beam current of 41 milliamps and the reflector voltage varied between 150 to 162 volts to operate at the center of the peak power reflector mode the curve labeled E in FIG. 13 resulted which had a 325 me. tunable band.

In FIG. 12 another alternative tuner embodiment is depicted which eliminates the support rod between the choke 61 and the tuner screw 85 with the screw O.D. reduced as shown. With L=.750 inch; guide I.D.=.385 inch; screw O.D.=.250 inch at a beam voltage of 300 volts with a beam current of 41 milliamps and a reflector voltage varied between 150 to 167 volts to peak the power by tuning to the center of the peak power reflector mode the curve F on FIG. 13 resulted which had a fairly flat 410 mc. tunable band.

Curve G in FIG. 13 resulted from the tuner embodiment depicted in FIG. 4 at a 300 volt beam voltage; 41 milliamp beam current; L=.75 inch; guide I.D.=.385 inch and a peak power reflector mode voltage variation of 150 to 158 volts to operate at the center of the peak power reflector mode over the tunable band.

The aforementioned Power vs. frequency mechanical tuning characteristics are merely presented as evidence of the wide range of slopes and bandwidths which can be achieved with the leaky wall H-field tuner concept of the present invention and are obviously not meant to be restrictive in any manner since it will be appreciated by those skilled in the art that an infinite variety of tuning characteristics can be obtained by variation of the tuner and tube physical and electrical parameters.

In FIGS. 14 and 15 a variation of the window-iris coupling means is depicted which includes an oblong shaped window 90 mounted on a copper or the like frame 91 disposed within a copper or the like keeper washer 47 with all parts brazed together to form a vacuum seal for oblong shaped iris 35. The frame 91 provides a more reliable vacuum seal because of its better expansion and flexibleness than the schemes in which the window is brazed directly to the washer. The variation window-iris coupling means depicted in FIGS. 14 and 15 is utilizable with any of the tuner embodiments depicted herein.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof it is intended that all matter con tained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A high frequency electron discharge device of the klystron type having a main body portion defining an evacuated envelope including an electron gun means having a cathode for generating an electron beam disposed at the upstream end portion and internally of the vacuum envelope of said device, a resonant cavity disposed downstream from said cathode means and provided with a pair of axially spaced beam coupling apertures through which said electron beam travels in operation, said resonant cavity being provided with an aperture in a side wall therein, said aperture having an electromagnetic wave permeable dielectric window vacuum sealed thereacross, a waveguide having a dominant mode cut-oif frequency which is above the operating frequency of the klystron over the tunable band of the fundamental mode of the resonant cavity disposed about said dielectric window externally of said evacuated resonant cavity, said below cut-off waveguide having a tuning member disposed therein which functions to control the resonant frequency of cavity as a function of tuning member position within said waveguide.

2. A high frequency electron discharge device of the klystron type incorporating cathode means for generating and directing an electron beam along a central beam axis,

at least one resonant cavity disposed about said central beam axis and provided with a pair of axially spaced beam coupling apertures through which said electron beam travels in operation, said resonant cavity being provided with an electromagnetic iris coupling aperture in one of the side walls thereof, said iris coupling aperture having a dielectric window permeable to electromagnetic energy disposed thereacross and forming a part of the vacuum envelope of said klystron device, a waveguide disposed about said dielectric window externally of said resonant cavity, said waveguide having a dominant mode cut-off frequency which is above the operating frequency of said klystron over the entire tunable band of the fundamental mode of said resonant cavity, said below cut-off waveguide being provided with means for varying the amount of electromagnetic energy coupled therein to thereby vary the operating frequency of said klystron.

3. A high frequency electron discharge device of the klystron type incorporating electron gun means disposed at the upstream end portion thereof for generating an electron beam and including at least one re-entrant resonant cavity disposed about said beam axis, said resonant cavity. being provided with an aperture in a side wall thereof, said aperture having an electromagnetic wave permeable dielectric window vacuum sealed therein such as to form part of the vacuum envelope of said device, a waveguide disposed externally of said resonant cavity and having internal cross-sectional dimensions which are dimensioned such that the waveguide has a dominant mode cut-off frequency which is above the operating frequency of the fundamental mode of the resonant cavity of the klystron, said below cut-01f waveguide having a tuning member disposed therein, said tuning member being movable within said below cut-off waveguide in a manner such that the resonant frequency of the resonant cavity may be varied with movement of said tuning probe by variation of the H-field penetration coupled into said waveguide from said resonant cavity.

4. A high frequency electron discharge device of the klystron type incorporating a resonant cavity having an aperture therein through which electromagnetic energy may be coupled, a dielectric window disposed across said aperture and forming a vacuum seal for said aperture, a waveguide dimensioned to have a dominant mode cut-off frequency which is greater than the operating frequency of the fundamental mode of said resonant cavity over the tunable range of the cavity While supporting the funda mental mode and disposed about said dielectric window externally of said vacuum envelope, said below cut-off Waveguide having means for varying the amount of electromagnetic H-field penetration therein from said resonant cavity in a manner such that the resonant frequency of said resonant cavity may be varied thereby.

5. A high frequency electron discharge device of the klystron type incorporating a re-entrant resonant cavity and operable in the fundamental mode of said re-entrant resonant cavity, said re-entrant resonant cavity having a pair of axially displaced end walls having axially aligned apertures therein for permitting an electron beam to pass axially through said re-entrant resonant cavity, said reentrant resonant cavity being provided with tuning means for varying the resonant frequency of said cavity, said tuning means being dispose-d external to the vacuum envelope of said klystron, said tuning means including a waveguide coupled to a side wall portion of said re-entrant resonant cavity via an aperture in said side wall, and through an electromagnetic wave permeable dielectric wind-ow forming a part of the vacuum envelope of said klystron, said waveguide being dimensioned to have a cut-off frequency which is above the highest operating frequency of the tunable bandwidth of said re-entrant resonant cavity while operating in the fundamental mode of said re-entrant resonant cavity, said tuning means further including tuning means disposed within said waveguide externally of the vacuum envelope of said klystron,

said tuning means functioning to vary the resonant frequency of said re-entrant resonant cavity primarily by variation of the amount of H-field penetration of the fundamental mode electromagnetic field pattern of said re-entrant resonant cavity within said below cut-off waveguide by movement of said tuning means disposed within said Waveguide.

6. The klystron device defined in claim 5 wherein said waveguide is circular and said tuning means is a screw having external threads, said circular waveguide being provided with internal threads for reception of said externally threaded screw.

7. The klystron device defined in claim 5 wherein said waveguide coupled to said re-entrant resonant cavity is circular and wherein said highest operating frequency of the tunable bandwidth of said re-entrant resonant cavity is below the cut-off frequency for the TE mode of said circular waveguide.

8. The klystron device defined in claim 5 wherein said waveguide is circular and said tuning means is an externally threaded dielectric screw and wherein said circular waveguide is provided with internal threads for reception of said externally threaded dielectric screw.

9. The klystron device defined in claim 5 wherein said dielectric window is circular and wherein said aperture in said side wall is an oblong shaped iris, said window being disposed in vacuum sealed relationship with respect to said klystron body by being brazed toan external surface portion thereof and by being disposed within and brazed to the central aperture in a deformable metal washer which washer is brazed to an external surface portion of said klystron body about said oblong shaped iris aperture.

10. The klystron defined in claim 5 wherein said waveguide is circular and said tuning means is an externally threaded metal screw having a reduced diameter end tip portion.

11. The klystron defined in claim 5 wherein said waveguide is circular and said tuning means is an externally threaded screw having a reduced diameter end tip portion made of dielectric material.

12. The klystron defined in claim 5 wherein said waveguide is circular and said tuning means is an externally threaded screw having a N4 choke disposed on the end portion thereof where is determined at any frequency within the operating band.

13. The klystron defined in claim 12 wherein said screw has an external diameter which is less than the internal diameter of said circular waveguide and wherein said M4 choke is mounted on a support rod protruding from the end of said screw, said support rod having a diameter Which is less than the external diameter of said screw.

14. The klystron defined in claim 12 wherein said screw has an external diameter which is less than the internal diameter of said circular waveguide and wherein said M4 choke is mounted on a M 2 support rod protruding from the end of said screw, said support rod having a diameter which is less than the external diameter of said :screw.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, In, Assistant Examiner. 

1. A HIGH FREQUENCY ELECTRON DISCHARGE DEVICE OF THE KLYSTRON TYPE HAVING A MAIN BODY PORTION DEFINING AN EVACUATED ENVELOPE INCLUDING AN ELECTRON GUN MEANS HAVING A CATHODE FOR GENERATING AN ELECTRON BEAM DISPOSED AT THE UPSTREAM END PORTION AND INTERNALLY OF THE VACUUM ENVELOPE OF SAID DEVICE, A RESONANT CAVITY DISPOSED DOWNSTREAM FROM SAID CATHODE MEANS AND PROVIDED WITH A PAIR OF AXIALLY SPACED BEAM COUPLING APERTURES THROUGH WHICH SAID ELECTRON BEAM TRAVELS IN OPERATION, SAID RESONANT CAVITY BEING PROVIDED WITH AN APERTURE IN A SIDE WALL THEREIN, SAID APERTURE HAVING AN ELECTROMAGNETIC WAVE PERMEABLE DIELECTRIC WINDOW VACUUM SEALED THEREACROSS, A WAVEGUIDE HAVING A DOMINANT MODE CUT-OFF FREQUENCY WHICH IS ABOVE THE OPERATING FREQUENCY OF THE KLYSTRON OVER THE TUNABLE BAND OF THE FUNDAMENTAL MODE OF THE RESONANT CAVITY DISPOSED ABOUT SAID DIELECTRIC WINDOW EXTERNALLY OF SAID EVACUATED RESONANT CAVITY, SAID BELOW CUT-OFF WAVEGUIDE HAVING A TUNING MEMBER DISPOSED THEREIN WHICH FUNCTIONS TO CONTROL THE RESONANT FREQUENCY OF CAVITY AS A FUNCTION OF TUNING MEMBER POSITION WITHIN SAID WAVEGUIDE. 